Environmental and economic pressures on the disposal of waste streams from two separate industries has led to the need to do more with these wastes than to bury them. The wastes are ash from coal-burning power plants, and spent lime (Precipitated Calcium Carbonate, or PCC) from sugar beet processing mills. The inventor has discovered that these disparate waste streams can be compatibly processed to create certain commercial products. Proper understanding of the invention for going beyond burial of these wastes requires certain distinctions, by type, among coal ashes:
1. "C" class fly ash is a fine powder residue from burnt coal that is captured by filtration from power plant flue gas. When mixed with water, it hardens like cement due to its pozzolanic mineralogy. Such mineralogy comes from the nature of certain sub-bituminous or lignite-type coals. The present use for C-class fly ash is limited mostly to that of an additive to portland cement and concrete, but much of the ash is buried in the ground. PA0 2. "F" class fly is a fine powder residue from burnt coal that is captured by filtration from power plant flue gas. When mixed with water it will not harden like cement because it contains unburned carbon and has a non-pozzolanic mineralogy. Most "F" class fly ash contains a significant amount of unburned carbon (which give sit a gray or black hue) and it is deficient in calcium oxide. Usually, it is the anthracite or bituminous coal which produces this type of ash. Most of this ash is buried in the ground. "F" class fly ash can be mixed with C-class fly ash to form a semi-hardened "flashfill" for trenches. It should also be noted that some F-class fly ash contains little or no unburned carbon, and can be used as an additive for portland cement. This kind of F-class ash will harden with water, but more slowly than C-class fly ash. PA0 3. Bottom ash is a granular or clinkery residue consisting of mostly silicon dioxide and aluminum oxide. Bottom ash collects in the bottoms of furnaces and boilers where the coal is burned and quenched with water before removal. Except for limited roadway uses, most of this ash is buried in the ground. PA0 4. In the beet sugar industry, hydrated lime is used to remove impurities from sugar made from beets. The precipitated lime (PCC) is placed in vast settling ponds and scooped into piles as it dries. This spent lime can be recalcined to calcium oxide (quicklime) by heating it to about 800-900.degree. C. for periods of about 10 to about 30 minutes, but generally this process is more expensive than the purchase of fresh hydrated lime, and so PCC is considered as a waste. Most often, huge piles of PCC are simply left in heaps on the ground. As processing continues, these waste piles continue to grow. PA0 5. To appreciate the present invention, it is also helpful to understand the process-origins of certain compounds in portland cement which give it its strength.
Pulverized limestone is the main constituent in portland cement. To the extent that the limestone lacks oxides of aluminum, silicon and iron, these minerals are added in the desired proportions at the time the calcination proceeds in cement processing. Calcination, or heating of the limestone, changes it chemically from CaCO.sub.3 to CaO. However, to obtain compounds such as dicalcium silicate and tricalcium silicate, which contribute to the strength of portland cement, the calcined mixture must be taken to the liquid, or melting phase. Generally, this will be in the range about 1,000.degree. C. When cooled, clinkers are formed that contain dicalcium silicate and tricalcium silicate. The clinkers are then crushed and milled into portland cement.
In the course of operation, it is common for paper mills to accumulate vast quantities of fibrous cellulose material in the settling ponds of their process water. Recent practice has been to skim and strain the fibrous matter from the pond water or to let the fibrous matter separate by evaporation. As a result of these processes, the cellulose fibers stick together in small clumps, forming paper wads or "pebbles", which can range in size from about 1/16 inch to about 11/2 inch. It has been the practice of the paper industry to windrow these "pebbles" for drying before plowing them into agricultural soils to help loosen the soil. However, this practice has had some negative cumulative effects on the environment because the paper material has trace amounts of environmentally offensive chemicals. Mills are now required to dispose of this material in a manner more friendly to the environment.
In the utility industry, there is a grade of coal ash known as "C" fly ash which is pozzolanic in its mineralogy. That is, "C" fly ash will harden like cement when water is added. Unlike cement, this hardening typically occurs within the space of a few minutes. The main use for this fly ash is as an additive to cement, but large amounts of the fly ash are still buried in the ground.
It would be advantageous to provide a means for producing a useful product utilizing predominately waste materials. It would particularly be advantageous to utilize waste cellulose fibers, such as from paper mill waste, and the waste fly ash from coal burning processes, to produce a commercially useful structural material.
It is becoming common practice in the construction of foundation walls to use interlocking lightweight polystyrene panels, supported by internal plastic brackets and external temporary bracing, as forms to receive concrete. The main advantage, from a building cost standpoint, is the reduction of labor costs associated with erecting the form and removing the form, as is the case with plywood panels. Polystyrene, which is kept in place after the concrete is poured, is insulative and water repellent. However, it offers some toxic smoke hazards on inside walls when subjected to fire. Moreover, the polystyrene is so lightweight that it offers no chance of mechanical attachment as with nails or screws, and it tends to bow or flex under pressure from the liquid concrete. To counteract this pressure, plastic retainers are fixed to pre-formed slots on the inside of the polystyrene panels to hold the wall forms to a consistent width against the outward pressure of the concrete. These plastic retainers form an interior lattice which also supports bars of reinforcing steel. When the concrete sets, the plastic and steel become integral with the concrete, continuing to hold the polystyrene to the wall surfaces.
The casting of concrete or other cementitious blocks or bricks which have multi-axial shaping or texturing on four or more sides by means of a single casting process usually requires multi-piece forms. Much of the casting difficulty lies in what is known as "release," that is, separating the form from the molded product quickly for the sake of mass production. This difficulty is compounded when casting an item which is "pierced," i.e., has one or more internal holes or cavities extending from one side to another. Quite often, very expensive equipment and multiple dies are required to achieve the desired effect, or milling may be necessary after casting.
It would be desirable to have methods for producing useful products which incorporate conventional waste materials derived from coal burning and/or sugar refining. The present invention in its various aspects, relates to processes and products that involve the use of such material.